Sheet metal shrinking and stretching machines are well known. These machines include a first set of four tool cartridges that are specifically for shrinking sheet metal, and a second set of four tool cartridges that are specifically for stretching sheet metal. Each cartridge has a jaw for compressible engaging and gripping a sheet metal workpiece. When the upper and lower jaws are separated, the sheet metal is placed between the gap between them. The operation of the machine brings the jaws into compressed engagement with the sheet metal, which is located between the upper and lower jaws. The jaws firmly hold the sheet metal in place between the upper and lower jaws. During shrinking mode, further compression of the jaws causes the right and left jaw sets to move toward each other so that a thin strip of the sheet metal between the right and left jaw sets is compressed or shrunk. During the stretching mode, further compression of the jaws causes the right and left jaw sets to move apart so that a thin strip of the sheet metal between the right and left jaw sets is stretched.
A problem with conventional shrinker stretcher machines is that switching from the shrinking mode to the stretching mode requires two tool units, each containing four tools, for a total of eight tools. One shrinker unit must be removed and replaced with a stretcher unit. The operator must have both tool units on hand in order to make the switch.
Another problem with conventional shrinker stretcher machines is that a shrinker unit includes four integral tools. If one tool in the shrinker unit breaks or becomes jammed, then the entire unit (all four tools) are rendered unusable. Similarly, if one tool in the stretcher unit breaks or becomes jammed, then the entire unit (all four tools) are rendered unusable. As a result, the efficient operation of a conventional shrinker stretcher machine typically requires one extra shrinker unit and one extra stretcher unit to be on hand to prevent costly machine down time. Yet, each shrinker unit and each stretcher unit is relatively expensive.
A still further problem with conventional shrinker stretcher machines is that each shrinker unit includes four integral jaws. Yet, different sheet metal thicknesses or materials such as aluminum, copper, copper-nickel, mild steel, steel, stainless steel work best with different types of jaw surfaces textures to grip the sheet metal during operation. Different jaw surface textures produce the different gripping power needed to shrink or stretch different materials or material thicknesses. In addition, some job specifications require minimal surface distortion to achieve a necessary level of smoothness in the finished workpiece. While a knurled or low grit jaw surface may work best for a particular material, material thickness or project specification, a serrated jaw surface may work best for another, and a large grit or hard grit or even diamond grit surface may work best for yet another. Yet, because the jaws are integral components of the shrinker or stretcher tool units for conventional shrinker stretcher machines, multiple shrinker tool units or stretcher tool units are required to effectively handle a wide variety of sheet metals materials, sheet metal thicknesses or project specifications.
A still further problem with conventional shrinker stretcher machines is their limited range of use. While the machines produce enough gripping power to adequate handle softer sheet metal materials, such as aluminum, copper, copper-nickel or mild steel, they do not produce enough gripping power to adequately handle harder materials, such as steel or stainless steel. The gripping power of many conventional machines also limits the thickness of the sheet metal workpieces they can handle, as thicker sheets require more gripping power to shrink or stretch the metal.
The present invention is intended to solve these and other problems.